The story
From constellational + -ly (suffix forming adverbs from adjectives).
Etymology from Wiktionary, CC BY-SA 4.0.
Today it means: In the manner of a constellation (“(astrology) the configuration of planets at a given time (notably of birth), as used for determining a horoscope; (astronomy) a formation of stars perceived as a figure or pattern”). Full definition →
From constellational + -ly (suffix forming adverbs from adjectives).
Etymology from Wiktionary, CC BY-SA 4.0.